| Re: Why is Jim Bounds push the 1 wire?? [message #369178 is a reply to message #369176] |
Sun, 20 March 2022 19:28   |
 |
RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma:
|
Senior Member |
|
|
JimB pushes the one-wire alternator as his solution to the Nichrome (resistor) portion of the alternator exciter wire getting hot and melting insulation in the wiring harness.
Matt, you know that the ONLY time current flows in the alternator exciter wire is when the alternator is not operating or there is a fault. The GEN light also comes ON during either of these conditions to alert the driver. So if the exciter wire has melted, there was a fault causing excess current to flow in it.
I suspect many of these faults are due to a failure in the Isolator. In this case the chassis voltage starts to drop and the alternator tries to compensate by raising the output voltage. The GEN light should turn ON to warn of this condition, however GM added a diode to cure the "Dim GEN" light issue that occurred when there was high current draw in the motorhome application. This diode will prevent the GEN light from coming ON during this failure. The APC cable will prevent the excess current draw in this failure mode, but also prevents the GEN light from coming ON. So the driver continues on blissfully unaware that there is a problem.
One-wire alternators are a fixed voltage output device. They work well in applications where the current draw from the alternator is low and more or less constant such as a fixed industrial/agricultural engine pumping water etc. They do not sense the voltage near the chassis battery, so they are not able to compensate for voltage losses due to varying current demands and also the voltage drop across the Isolator and hence the batteries do not get fully charged.
I suspect most owners with a one-wire alternator are unaware that their batteries are getting less than a full charge. As long as there is enough charge in the engine battery to start it and enough charge in the house batteries to get through a night of dry camping. They might notice their dash HVAC fan does not run as fast, especially on high, or that their headlights are not as bright, or that the headlights dim and fan slows with the operation of the turn signals.
I had my alternator go south while on the way to have the transmission issue fixed. I asked them to replace the alternator at the same time (it was 12 years old so it had a good run) On the way home my DigiPanel was showing low voltage with an orange light on the voltage bar. It turned out the alternator shop sent him a one-wire alternator as a replacement. I had asked for my old alternator back so I could repair it for a spare. After fixing the old alternator and swapping it back into service, I opened the new alternator. Sure enough it was a one-wire regulator in it. I replaced the regulator with a proper 3- wire 14.5V regulator and now it is my spare.
I bypassed my nichrome wire with a clearance light assembly and mounted it under the dash where I can see it. This lamp gives the extra exciter current during startup and will also come ON to warn of a alternator failure (my 1977 has the dash GEN diode).
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
|
|
|
|
GMCforum
Search
Help
Register
Login
Home
